/**
 * @file
 * Address Resolution Protocol module for IP over Ethernet
 *
 * Functionally, ARP is divided into two parts. The first maps an IP address
 * to a physical address when sending a packet, and the second part answers
 * requests from other machines for our physical address.
 *
 * This implementation complies with RFC 826 (Ethernet ARP). It supports
 * Gratuitious ARP from RFC3220 (IP Mobility Support for IPv4) section 4.6
 * if an interface calls etharp_gratuitous(our_netif) upon address change.
 */

/*
 * Copyright (c) 2001-2003 Swedish Institute of Computer Science.
 * Copyright (c) 2003-2004 Leon Woestenberg <leon.woestenberg@axon.tv>
 * Copyright (c) 2003-2004 Axon Digital Design B.V., The Netherlands.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 */


#include "lwip/opt.h"

#if LWIP_ARP /* don't build if not configured for use in lwipopts.h */

#include "lwip/inet.h"
#include "lwip/ip.h"
#include "lwip/stats.h"
#include "lwip/snmp.h"
#include "lwip/dhcp.h"
#include "lwip/autoip.h"
#include "netif/etharp.h"

#if PPPOE_SUPPORT
#include "netif/ppp_oe.h"
#endif /* PPPOE_SUPPORT */

#include <string.h>
#include <stdlib.h>

/** the time an ARP entry stays valid after its last update,
 *  for ARP_TMR_INTERVAL = 5000, this is
 *  (240 * 5) seconds = 20 minutes.
 */
#define ARP_MAXAGE 240
/** the time an ARP entry stays pending after first request,
 *  for ARP_TMR_INTERVAL = 5000, this is
 *  (2 * 5) seconds = 10 seconds.
 *
 *  @internal Keep this number at least 2, otherwise it might
 *  run out instantly if the timeout occurs directly after a request.
 */
#define ARP_MAXPENDING 2

#define HWTYPE_ETHERNET 1

#define ARPH_HWLEN(hdr) (ntohs((hdr)->_hwlen_protolen) >> 8)
#define ARPH_PROTOLEN(hdr) (ntohs((hdr)->_hwlen_protolen) & 0xff)

#define ARPH_HWLEN_SET(hdr, len) (hdr)->_hwlen_protolen = htons(ARPH_PROTOLEN(hdr) | ((len) << 8))
#define ARPH_PROTOLEN_SET(hdr, len) (hdr)->_hwlen_protolen = htons((len) | (ARPH_HWLEN(hdr) << 8))

enum etharp_state
{
    ETHARP_STATE_EMPTY = 0,
    ETHARP_STATE_PENDING,
    ETHARP_STATE_STABLE
};

struct etharp_entry
{
#if ARP_QUEUEING
    /**
     * Pointer to queue of pending outgoing packets on this ARP entry.
     */
    struct etharp_q_entry *q;
#endif
    struct ip_addr ipaddr;
    struct eth_addr ethaddr;
    enum etharp_state state;
    u8_t ctime;
    struct netif *netif;
};

const struct eth_addr ethbroadcast = { { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff } };
const struct eth_addr ethzero = { { 0, 0, 0, 0, 0, 0 } };
static struct etharp_entry arp_table[ARP_TABLE_SIZE];
#if !LWIP_NETIF_HWADDRHINT
static u8_t etharp_cached_entry;
#endif

/**
 * Try hard to create a new entry - we want the IP address to appear in
 * the cache (even if this means removing an active entry or so). */
#define ETHARP_TRY_HARD 1
#define ETHARP_FIND_ONLY  2

#if LWIP_NETIF_HWADDRHINT
#define NETIF_SET_HINT(netif, hint)  if (((netif) != NULL) && ((netif)->addr_hint != NULL)) {  \
        *((netif)->addr_hint) = (hint); }
static s8_t find_entry(struct ip_addr *ipaddr, u8_t flags, struct netif *netif);
#else /* LWIP_NETIF_HWADDRHINT */
static s8_t find_entry(struct ip_addr *ipaddr, u8_t flags);
#endif /* LWIP_NETIF_HWADDRHINT */

static err_t update_arp_entry(struct netif *netif, struct ip_addr *ipaddr, struct eth_addr *ethaddr, u8_t flags);


/* Some checks, instead of etharp_init(): */
#if (LWIP_ARP && (ARP_TABLE_SIZE > 0x7f))
  #error "If you want to use ARP, ARP_TABLE_SIZE must fit in an s8_t, so, you have to reduce it in your lwipopts.h"
#endif


#if ARP_QUEUEING
/**
 * Free a complete queue of etharp entries
 *
 * @param q a qeueue of etharp_q_entry's to free
 */
static void
free_etharp_q(struct etharp_q_entry *q)
{
    struct etharp_q_entry *r;

    LWIP_ASSERT("q != NULL", q != NULL);
    LWIP_ASSERT("q->p != NULL", q->p != NULL);
    while (q)
    {
        r = q;
        q = q->next;
        LWIP_ASSERT("r->p != NULL", (r->p != NULL));
        pbuf_free(r->p);
        memp_free(MEMP_ARP_QUEUE, r);
    }
}
#endif

/**
 * Clears expired entries in the ARP table.
 *
 * This function should be called every ETHARP_TMR_INTERVAL microseconds (5 seconds),
 * in order to expire entries in the ARP table.
 */
void
etharp_tmr(void)
{
    u8_t i;

    LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer\n"));
    /* remove expired entries from the ARP table */
    for (i = 0; i < ARP_TABLE_SIZE; ++i)
    {
        arp_table[i].ctime++;
        if (((arp_table[i].state == ETHARP_STATE_STABLE) &&
             (arp_table[i].ctime >= ARP_MAXAGE)) ||
            ((arp_table[i].state == ETHARP_STATE_PENDING)  &&
             (arp_table[i].ctime >= ARP_MAXPENDING)))
        {
            /* pending or stable entry has become old! */
            LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired %s entry %"U 16_F ".\n",
                                       arp_table[i].state == ETHARP_STATE_STABLE ? "stable" : "pending", (u16_t)i));
            /* clean up entries that have just been expired */
            /* remove from SNMP ARP index tree */
            snmp_delete_arpidx_tree(arp_table[i].netif, &arp_table[i].ipaddr);
#if ARP_QUEUEING
            /* and empty packet queue */
            if (arp_table[i].q != NULL)
            {
                /* remove all queued packets */
                LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: freeing entry %"U 16_F ", packet queue %p.\n", (u16_t)i, (void*)(arp_table[i].q)));
                free_etharp_q(arp_table[i].q);
                arp_table[i].q = NULL;
            }
#endif
            /* recycle entry for re-use */
            arp_table[i].state = ETHARP_STATE_EMPTY;
        }
#if ARP_QUEUEING
        /* still pending entry? (not expired) */
        if (arp_table[i].state == ETHARP_STATE_PENDING)
        {
            /* resend an ARP query here? */
        }
#endif
    }
}

/**
 * Search the ARP table for a matching or new entry.
 *
 * If an IP address is given, return a pending or stable ARP entry that matches
 * the address. If no match is found, create a new entry with this address set,
 * but in state ETHARP_EMPTY. The caller must check and possibly change the
 * state of the returned entry.
 *
 * If ipaddr is NULL, return a initialized new entry in state ETHARP_EMPTY.
 *
 * In all cases, attempt to create new entries from an empty entry. If no
 * empty entries are available and ETHARP_TRY_HARD flag is set, recycle
 * old entries. Heuristic choose the least important entry for recycling.
 *
 * @param ipaddr IP address to find in ARP cache, or to add if not found.
 * @param flags
 * - ETHARP_TRY_HARD: Try hard to create a entry by allowing recycling of
 * active (stable or pending) entries.
 *
 * @return The ARP entry index that matched or is created, ERR_MEM if no
 * entry is found or could be recycled.
 */
static s8_t
#if LWIP_NETIF_HWADDRHINT
find_entry(struct ip_addr *ipaddr, u8_t flags, struct netif *netif)
#else /* LWIP_NETIF_HWADDRHINT */
find_entry(struct ip_addr *ipaddr, u8_t flags)
#endif /* LWIP_NETIF_HWADDRHINT */
{
    s8_t old_pending = ARP_TABLE_SIZE, old_stable = ARP_TABLE_SIZE;
    s8_t empty = ARP_TABLE_SIZE;
    u8_t i = 0, age_pending = 0, age_stable = 0;

#if ARP_QUEUEING
    /* oldest entry with packets on queue */
    s8_t old_queue = ARP_TABLE_SIZE;
    /* its age */
    u8_t age_queue = 0;
#endif

    /* First, test if the last call to this function asked for the
     * same address. If so, we're really fast! */
    if (ipaddr)
    {
        /* ipaddr to search for was given */
#if LWIP_NETIF_HWADDRHINT
        if ((netif != NULL) && (netif->addr_hint != NULL))
        {
            /* per-pcb cached entry was given */
            u8_t per_pcb_cache = *(netif->addr_hint);
            if ((per_pcb_cache < ARP_TABLE_SIZE) && arp_table[per_pcb_cache].state == ETHARP_STATE_STABLE)
            {
                /* the per-pcb-cached entry is stable */
                if (ip_addr_cmp(ipaddr, &arp_table[per_pcb_cache].ipaddr))
                {
                    /* per-pcb cached entry was the right one! */
                    ETHARP_STATS_INC(etharp.cachehit);
                    return per_pcb_cache;
                }
            }
        }
#else   /* #if LWIP_NETIF_HWADDRHINT */
        if (arp_table[etharp_cached_entry].state == ETHARP_STATE_STABLE)
        {
            /* the cached entry is stable */
            if (ip_addr_cmp(ipaddr, &arp_table[etharp_cached_entry].ipaddr))
            {
                /* cached entry was the right one! */
                ETHARP_STATS_INC(etharp.cachehit);
                return etharp_cached_entry;
            }
        }
#endif  /* #if LWIP_NETIF_HWADDRHINT */
    }

    /**
     * a) do a search through the cache, remember candidates
     * b) select candidate entry
     * c) create new entry
     */

    /* a) in a single search sweep, do all of this
     * 1) remember the first empty entry (if any)
     * 2) remember the oldest stable entry (if any)
     * 3) remember the oldest pending entry without queued packets (if any)
     * 4) remember the oldest pending entry with queued packets (if any)
     * 5) search for a matching IP entry, either pending or stable
     *    until 5 matches, or all entries are searched for.
     */

    for (i = 0; i < ARP_TABLE_SIZE; ++i)
    {
        /* no empty entry found yet and now we do find one? */
        if ((empty == ARP_TABLE_SIZE) && (arp_table[i].state == ETHARP_STATE_EMPTY))
        {
            LWIP_DEBUGF(ETHARP_DEBUG, ("find_entry: found empty entry %"U 16_F "\n", (u16_t)i));
            /* remember first empty entry */
            empty = i;
        }
        /* pending entry? */
        else if (arp_table[i].state == ETHARP_STATE_PENDING)
        {
            /* if given, does IP address match IP address in ARP entry? */
            if (ipaddr && ip_addr_cmp(ipaddr, &arp_table[i].ipaddr))
            {
                LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: found matching pending entry %"U 16_F "\n", (u16_t)i));
                /* found exact IP address match, simply bail out */
#if LWIP_NETIF_HWADDRHINT
                NETIF_SET_HINT(netif, i);
#else           /* #if LWIP_NETIF_HWADDRHINT */
                etharp_cached_entry = i;
#endif /* #if LWIP_NETIF_HWADDRHINT */
                return i;
#if ARP_QUEUEING
                /* pending with queued packets? */
            }
            else if (arp_table[i].q != NULL)
            {
                if (arp_table[i].ctime >= age_queue)
                {
                    old_queue = i;
                    age_queue = arp_table[i].ctime;
                }
#endif
                /* pending without queued packets? */
            }
            else
            {
                if (arp_table[i].ctime >= age_pending)
                {
                    old_pending = i;
                    age_pending = arp_table[i].ctime;
                }
            }
        }
        /* stable entry? */
        else if (arp_table[i].state == ETHARP_STATE_STABLE)
        {
            /* if given, does IP address match IP address in ARP entry? */
            if (ipaddr && ip_addr_cmp(ipaddr, &arp_table[i].ipaddr))
            {
                LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: found matching stable entry %"U 16_F "\n", (u16_t)i));
                /* found exact IP address match, simply bail out */
#if LWIP_NETIF_HWADDRHINT
                NETIF_SET_HINT(netif, i);
#else           /* #if LWIP_NETIF_HWADDRHINT */
                etharp_cached_entry = i;
#endif /* #if LWIP_NETIF_HWADDRHINT */
                return i;
                /* remember entry with oldest stable entry in oldest, its age in maxtime */
            }
            else if (arp_table[i].ctime >= age_stable)
            {
                old_stable = i;
                age_stable = arp_table[i].ctime;
            }
        }
    }
    /* { we have no match } => try to create a new entry */

    /* no empty entry found and not allowed to recycle? */
    if (((empty == ARP_TABLE_SIZE) && ((flags & ETHARP_TRY_HARD) == 0))
        /* or don't create new entry, only search? */
        || ((flags & ETHARP_FIND_ONLY) != 0))
    {
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: no empty entry found and not allowed to recycle\n"));
        return (s8_t)ERR_MEM;
    }

    /* b) choose the least destructive entry to recycle:
     * 1) empty entry
     * 2) oldest stable entry
     * 3) oldest pending entry without queued packets
     * 4) oldest pending entry with queued packets
     *
     * { ETHARP_TRY_HARD is set at this point }
     */

    /* 1) empty entry available? */
    if (empty < ARP_TABLE_SIZE)
    {
        i = empty;
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting empty entry %"U 16_F "\n", (u16_t)i));
    }
    /* 2) found recyclable stable entry? */
    else if (old_stable < ARP_TABLE_SIZE)
    {
        /* recycle oldest stable*/
        i = old_stable;
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest stable entry %"U 16_F "\n", (u16_t)i));
#if ARP_QUEUEING
        /* no queued packets should exist on stable entries */
        LWIP_ASSERT("arp_table[i].q == NULL", arp_table[i].q == NULL);
#endif
        /* 3) found recyclable pending entry without queued packets? */
    }
    else if (old_pending < ARP_TABLE_SIZE)
    {
        /* recycle oldest pending */
        i = old_pending;
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest pending entry %"U 16_F " (without queue)\n", (u16_t)i));
#if ARP_QUEUEING
        /* 4) found recyclable pending entry with queued packets? */
    }
    else if (old_queue < ARP_TABLE_SIZE)
    {
        /* recycle oldest pending */
        i = old_queue;
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest pending entry %"U 16_F ", freeing packet queue %p\n", (u16_t)i, (void*)(arp_table[i].q)));
        free_etharp_q(arp_table[i].q);
        arp_table[i].q = NULL;
#endif
        /* no empty or recyclable entries found */
    }
    else
    {
        return (s8_t)ERR_MEM;
    }

    /* { empty or recyclable entry found } */
    LWIP_ASSERT("i < ARP_TABLE_SIZE", i < ARP_TABLE_SIZE);

    if (arp_table[i].state != ETHARP_STATE_EMPTY)
    {
        snmp_delete_arpidx_tree(arp_table[i].netif, &arp_table[i].ipaddr);
    }
    /* recycle entry (no-op for an already empty entry) */
    arp_table[i].state = ETHARP_STATE_EMPTY;

    /* IP address given? */
    if (ipaddr != NULL)
    {
        /* set IP address */
        ip_addr_set(&arp_table[i].ipaddr, ipaddr);
    }
    arp_table[i].ctime = 0;
#if LWIP_NETIF_HWADDRHINT
    NETIF_SET_HINT(netif, i);
#else /* #if LWIP_NETIF_HWADDRHINT */
    etharp_cached_entry = i;
#endif /* #if LWIP_NETIF_HWADDRHINT */
    return (err_t)i;
}

/**
 * Send an IP packet on the network using netif->linkoutput
 * The ethernet header is filled in before sending.
 *
 * @params netif the lwIP network interface on which to send the packet
 * @params p the packet to send, p->payload pointing to the (uninitialized) ethernet header
 * @params src the source MAC address to be copied into the ethernet header
 * @params dst the destination MAC address to be copied into the ethernet header
 * @return ERR_OK if the packet was sent, any other err_t on failure
 */
static err_t
etharp_send_ip(struct netif *netif, struct pbuf *p, struct eth_addr *src, struct eth_addr *dst)
{
    struct eth_hdr *ethhdr = p->payload;
    u8_t k;

    LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
                (netif->hwaddr_len == ETHARP_HWADDR_LEN));
    k = ETHARP_HWADDR_LEN;
    while (k > 0)
    {
        k--;
        ethhdr->dest.addr[k] = dst->addr[k];
        ethhdr->src.addr[k]  = src->addr[k];
    }
    ethhdr->type = htons(ETHTYPE_IP);
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_send_ip: sending packet %p\n", (void*)p));
    /* send the packet */
    return netif->linkoutput(netif, p);
}

/**
 * Update (or insert) a IP/MAC address pair in the ARP cache.
 *
 * If a pending entry is resolved, any queued packets will be sent
 * at this point.
 *
 * @param ipaddr IP address of the inserted ARP entry.
 * @param ethaddr Ethernet address of the inserted ARP entry.
 * @param flags Defines behaviour:
 * - ETHARP_TRY_HARD Allows ARP to insert this as a new item. If not specified,
 * only existing ARP entries will be updated.
 *
 * @return
 * - ERR_OK Succesfully updated ARP cache.
 * - ERR_MEM If we could not add a new ARP entry when ETHARP_TRY_HARD was set.
 * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
 *
 * @see pbuf_free()
 */
static err_t
update_arp_entry(struct netif *netif, struct ip_addr *ipaddr, struct eth_addr *ethaddr, u8_t flags)
{
    s8_t i;
    u8_t k;

    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry()\n"));
    LWIP_ASSERT("netif->hwaddr_len == ETHARP_HWADDR_LEN", netif->hwaddr_len == ETHARP_HWADDR_LEN);
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry: %"U 16_F ".%"U 16_F ".%"U 16_F ".%"U 16_F " - %02"X 16_F ":%02"X 16_F ":%02"X 16_F ":%02"X 16_F ":%02"X 16_F ":%02"X 16_F "\n",
                                                ip4_addr1(ipaddr), ip4_addr2(ipaddr), ip4_addr3(ipaddr), ip4_addr4(ipaddr),
                                                ethaddr->addr[0], ethaddr->addr[1], ethaddr->addr[2],
                                                ethaddr->addr[3], ethaddr->addr[4], ethaddr->addr[5]));
    /* non-unicast address? */
    if (ip_addr_isany(ipaddr) ||
        ip_addr_isbroadcast(ipaddr, netif) ||
        ip_addr_ismulticast(ipaddr))
    {
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry: will not add non-unicast IP address to ARP cache\n"));
        return ERR_ARG;
    }
    /* find or create ARP entry */
#if LWIP_NETIF_HWADDRHINT
    i = find_entry(ipaddr, flags, netif);
#else /* LWIP_NETIF_HWADDRHINT */
    i = find_entry(ipaddr, flags);
#endif /* LWIP_NETIF_HWADDRHINT */
       /* bail out if no entry could be found */
    if (i < 0)
    {
        return (err_t)i;
    }

    /* mark it stable */
    arp_table[i].state = ETHARP_STATE_STABLE;
    /* record network interface */
    arp_table[i].netif = netif;

    /* insert in SNMP ARP index tree */
    snmp_insert_arpidx_tree(netif, &arp_table[i].ipaddr);

    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry: updating stable entry %"S 16_F "\n", (s16_t)i));
    /* update address */
    k = ETHARP_HWADDR_LEN;
    while (k > 0)
    {
        k--;
        arp_table[i].ethaddr.addr[k] = ethaddr->addr[k];
    }
    /* reset time stamp */
    arp_table[i].ctime = 0;
#if ARP_QUEUEING
    /* this is where we will send out queued packets! */
    while (arp_table[i].q != NULL)
    {
        struct pbuf *p;
        /* remember remainder of queue */
        struct etharp_q_entry *q = arp_table[i].q;
        /* pop first item off the queue */
        arp_table[i].q = q->next;
        /* get the packet pointer */
        p = q->p;
        /* now queue entry can be freed */
        memp_free(MEMP_ARP_QUEUE, q);
        /* send the queued IP packet */
        etharp_send_ip(netif, p, (struct eth_addr*)(netif->hwaddr), ethaddr);
        /* free the queued IP packet */
        pbuf_free(p);
    }
#endif
    return ERR_OK;
}

/**
 * Finds (stable) ethernet/IP address pair from ARP table
 * using interface and IP address index.
 * @note the addresses in the ARP table are in network order!
 *
 * @param netif points to interface index
 * @param ipaddr points to the (network order) IP address index
 * @param eth_ret points to return pointer
 * @param ip_ret points to return pointer
 * @return table index if found, -1 otherwise
 */
s8_t
etharp_find_addr(struct netif *netif, struct ip_addr *ipaddr,
                 struct eth_addr **eth_ret, struct ip_addr **ip_ret)
{
    s8_t i;

    LWIP_UNUSED_ARG(netif);

#if LWIP_NETIF_HWADDRHINT
    i = find_entry(ipaddr, ETHARP_FIND_ONLY, NULL);
#else /* LWIP_NETIF_HWADDRHINT */
    i = find_entry(ipaddr, ETHARP_FIND_ONLY);
#endif /* LWIP_NETIF_HWADDRHINT */
    if ((i >= 0) && arp_table[i].state == ETHARP_STATE_STABLE)
    {
        *eth_ret = &arp_table[i].ethaddr;
        *ip_ret = &arp_table[i].ipaddr;
        return i;
    }
    return -1;
}

/**
 * Updates the ARP table using the given IP packet.
 *
 * Uses the incoming IP packet's source address to update the
 * ARP cache for the local network. The function does not alter
 * or free the packet. This function must be called before the
 * packet p is passed to the IP layer.
 *
 * @param netif The lwIP network interface on which the IP packet pbuf arrived.
 * @param p The IP packet that arrived on netif.
 *
 * @return NULL
 *
 * @see pbuf_free()
 */
void
etharp_ip_input(struct netif *netif, struct pbuf *p)
{
    struct eth_hdr *ethhdr;
    struct ip_hdr *iphdr;

    LWIP_ERROR("netif != NULL", (netif != NULL), return; );
    /* Only insert an entry if the source IP address of the
       incoming IP packet comes from a host on the local network. */
    ethhdr = p->payload;
    iphdr = (struct ip_hdr*)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
#if ETHARP_SUPPORT_VLAN
    if (ethhdr->type == ETHTYPE_VLAN)
    {
        iphdr = (struct ip_hdr*)((u8_t*)ethhdr + SIZEOF_ETH_HDR + SIZEOF_VLAN_HDR);
    }
#endif /* ETHARP_SUPPORT_VLAN */

    /* source is not on the local network? */
    if (!ip_addr_netcmp(&(iphdr->src), &(netif->ip_addr), &(netif->netmask)))
    {
        /* do nothing */
        return;
    }

    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_ip_input: updating ETHARP table.\n"));
    /* update ARP table */
    /* @todo We could use ETHARP_TRY_HARD if we think we are going to talk
     * back soon (for example, if the destination IP address is ours. */
    update_arp_entry(netif, &(iphdr->src), &(ethhdr->src), 0);
}


/**
 * Responds to ARP requests to us. Upon ARP replies to us, add entry to cache
 * send out queued IP packets. Updates cache with snooped address pairs.
 *
 * Should be called for incoming ARP packets. The pbuf in the argument
 * is freed by this function.
 *
 * @param netif The lwIP network interface on which the ARP packet pbuf arrived.
 * @param ethaddr Ethernet address of netif.
 * @param p The ARP packet that arrived on netif. Is freed by this function.
 *
 * @return NULL
 *
 * @see pbuf_free()
 */
void
etharp_arp_input(struct netif *netif, struct eth_addr *ethaddr, struct pbuf *p)
{
    struct etharp_hdr *hdr;
    struct eth_hdr *ethhdr;
    /* these are aligned properly, whereas the ARP header fields might not be */
    struct ip_addr sipaddr, dipaddr;
    u8_t i;
    u8_t for_us;

#if LWIP_AUTOIP
    const u8_t * ethdst_hwaddr;
#endif /* LWIP_AUTOIP */

    LWIP_ERROR("netif != NULL", (netif != NULL), return; );

    /* drop short ARP packets: we have to check for p->len instead of p->tot_len here
       since a struct etharp_hdr is pointed to p->payload, so it musn't be chained! */
    if (p->len < SIZEOF_ETHARP_PACKET)
    {
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                    ("etharp_arp_input: packet dropped, too short (%"S 16_F "/%"S 16_F ")\n", p->tot_len,
                     (s16_t)SIZEOF_ETHARP_PACKET));
        ETHARP_STATS_INC(etharp.lenerr);
        ETHARP_STATS_INC(etharp.drop);
        pbuf_free(p);
        return;
    }

    ethhdr = p->payload;
    hdr = (struct etharp_hdr*)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
#if ETHARP_SUPPORT_VLAN
    if (ethhdr->type == ETHTYPE_VLAN)
    {
        hdr = (struct etharp_hdr*)(((u8_t*)ethhdr) + SIZEOF_ETH_HDR + SIZEOF_VLAN_HDR);
    }
#endif /* ETHARP_SUPPORT_VLAN */

    /* RFC 826 "Packet Reception": */
    if ((hdr->hwtype != htons(HWTYPE_ETHERNET)) ||
        (hdr->_hwlen_protolen != htons((ETHARP_HWADDR_LEN << 8) | sizeof(struct ip_addr))) ||
        (hdr->proto != htons(ETHTYPE_IP)) ||
        (ethhdr->type != htons(ETHTYPE_ARP)))
    {
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                    ("etharp_arp_input: packet dropped, wrong hw type, hwlen, proto, protolen or ethernet type (%"U 16_F "/%"U 16_F "/%"U 16_F "/%"U 16_F "/%"U 16_F ")\n",
                     hdr->hwtype, ARPH_HWLEN(hdr), hdr->proto, ARPH_PROTOLEN(hdr), ethhdr->type));
        ETHARP_STATS_INC(etharp.proterr);
        ETHARP_STATS_INC(etharp.drop);
        pbuf_free(p);
        return;
    }
    ETHARP_STATS_INC(etharp.recv);

#if LWIP_AUTOIP
    /* We have to check if a host already has configured our random
     * created link local address and continously check if there is
     * a host with this IP-address so we can detect collisions */
    autoip_arp_reply(netif, hdr);
#endif /* LWIP_AUTOIP */

    /* Copy struct ip_addr2 to aligned ip_addr, to support compilers without
     * structure packing (not using structure copy which breaks strict-aliasing rules). */
    SMEMCPY(&sipaddr, &hdr->sipaddr, sizeof(sipaddr));
    SMEMCPY(&dipaddr, &hdr->dipaddr, sizeof(dipaddr));

    /* this interface is not configured? */
    if (netif->ip_addr.addr == 0)
    {
        for_us = 0;
    }
    else
    {
        /* ARP packet directed to us? */
        for_us = ip_addr_cmp(&dipaddr, &(netif->ip_addr));
    }

    /* ARP message directed to us? */
    if (for_us)
    {
        /* add IP address in ARP cache; assume requester wants to talk to us.
        * can result in directly sending the queued packets for this host. */
        update_arp_entry(netif, &sipaddr, &(hdr->shwaddr), ETHARP_TRY_HARD);
        /* ARP message not directed to us? */
    }
    else
    {
        /* update the source IP address in the cache, if present */
        update_arp_entry(netif, &sipaddr, &(hdr->shwaddr), 0);
    }

    /* now act on the message itself */
    switch (htons(hdr->opcode))
    {
    /* ARP request? */
    case ARP_REQUEST:
        /* ARP request. If it asked for our address, we send out a
         * reply. In any case, we time-stamp any existing ARP entry,
         * and possiby send out an IP packet that was queued on it. */

        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: incoming ARP request\n"));
        /* ARP request for our address? */
        if (for_us)
        {

            LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: replying to ARP request for our IP address\n"));
            /* Re-use pbuf to send ARP reply.
               Since we are re-using an existing pbuf, we can't call etharp_raw since
               that would allocate a new pbuf. */
            hdr->opcode = htons(ARP_REPLY);

            hdr->dipaddr = hdr->sipaddr;
            SMEMCPY(&hdr->sipaddr, &netif->ip_addr, sizeof(hdr->sipaddr));

            LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
                        (netif->hwaddr_len == ETHARP_HWADDR_LEN));
            i = ETHARP_HWADDR_LEN;
#if LWIP_AUTOIP
            /* If we are using Link-Local, ARP packets must be broadcast on the
             * link layer. (See RFC3927 Section 2.5) */
            ethdst_hwaddr = ((netif->autoip != NULL) && (netif->autoip->state != AUTOIP_STATE_OFF)) ? (u8_t*)(ethbroadcast.addr) : hdr->shwaddr.addr;
#endif      /* LWIP_AUTOIP */

            while (i > 0)
            {
                i--;
                hdr->dhwaddr.addr[i] = hdr->shwaddr.addr[i];
#if LWIP_AUTOIP
                ethhdr->dest.addr[i] = ethdst_hwaddr[i];
#else           /* LWIP_AUTOIP */
                ethhdr->dest.addr[i] = hdr->shwaddr.addr[i];
#endif /* LWIP_AUTOIP */
                hdr->shwaddr.addr[i] = ethaddr->addr[i];
                ethhdr->src.addr[i] = ethaddr->addr[i];
            }

            /* hwtype, hwaddr_len, proto, protolen and the type in the ethernet header
               are already correct, we tested that before */

            /* return ARP reply */
            netif->linkoutput(netif, p);
            /* we are not configured? */
        }
        else if (netif->ip_addr.addr == 0)
        {
            /* { for_us == 0 and netif->ip_addr.addr == 0 } */
            LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: we are unconfigured, ARP request ignored.\n"));
            /* request was not directed to us */
        }
        else
        {
            /* { for_us == 0 and netif->ip_addr.addr != 0 } */
            LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: ARP request was not for us.\n"));
        }
        break;
    case ARP_REPLY:
        /* ARP reply. We already updated the ARP cache earlier. */
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: incoming ARP reply\n"));
#if (LWIP_DHCP && DHCP_DOES_ARP_CHECK)
        /* DHCP wants to know about ARP replies from any host with an
         * IP address also offered to us by the DHCP server. We do not
         * want to take a duplicate IP address on a single network.
         * @todo How should we handle redundant (fail-over) interfaces? */
        dhcp_arp_reply(netif, &sipaddr);
#endif
        break;
    default:
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: ARP unknown opcode type %"S 16_F "\n", htons(hdr->opcode)));
        ETHARP_STATS_INC(etharp.err);
        break;
    }
    /* free ARP packet */
    pbuf_free(p);
}

/**
 * Resolve and fill-in Ethernet address header for outgoing IP packet.
 *
 * For IP multicast and broadcast, corresponding Ethernet addresses
 * are selected and the packet is transmitted on the link.
 *
 * For unicast addresses, the packet is submitted to etharp_query(). In
 * case the IP address is outside the local network, the IP address of
 * the gateway is used.
 *
 * @param netif The lwIP network interface which the IP packet will be sent on.
 * @param q The pbuf(s) containing the IP packet to be sent.
 * @param ipaddr The IP address of the packet destination.
 *
 * @return
 * - ERR_RTE No route to destination (no gateway to external networks),
 * or the return type of either etharp_query() or etharp_send_ip().
 */
err_t
etharp_output(struct netif *netif, struct pbuf *q, struct ip_addr *ipaddr)
{
    struct eth_addr *dest, mcastaddr;

    /* make room for Ethernet header - should not fail */
    if (pbuf_header(q, sizeof(struct eth_hdr)) != 0)
    {
        /* bail out */
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
                    ("etharp_output: could not allocate room for header.\n"));
        LINK_STATS_INC(link.lenerr);
        return ERR_BUF;
    }

    /* assume unresolved Ethernet address */
    dest = NULL;
    /* Determine on destination hardware address. Broadcasts and multicasts
     * are special, other IP addresses are looked up in the ARP table. */

    /* broadcast destination IP address? */
    if (ip_addr_isbroadcast(ipaddr, netif))
    {
        /* broadcast on Ethernet also */
        dest = (struct eth_addr*)&ethbroadcast;
        /* multicast destination IP address? */
    }
    else if (ip_addr_ismulticast(ipaddr))
    {
        /* Hash IP multicast address to MAC address.*/
        mcastaddr.addr[0] = 0x01;
        mcastaddr.addr[1] = 0x00;
        mcastaddr.addr[2] = 0x5e;
        mcastaddr.addr[3] = ip4_addr2(ipaddr) & 0x7f;
        mcastaddr.addr[4] = ip4_addr3(ipaddr);
        mcastaddr.addr[5] = ip4_addr4(ipaddr);
        /* destination Ethernet address is multicast */
        dest = &mcastaddr;
        /* unicast destination IP address? */
    }
    else
    {
        /* outside local network? */
        if (!ip_addr_netcmp(ipaddr, &(netif->ip_addr), &(netif->netmask)))
        {
            /* interface has default gateway? */
            if (netif->gw.addr != 0)
            {
                /* send to hardware address of default gateway IP address */
                ipaddr = &(netif->gw);
                /* no default gateway available */
            }
            else
            {
                /* no route to destination error (default gateway missing) */
                return ERR_RTE;
            }
        }
        /* queue on destination Ethernet address belonging to ipaddr */
        return etharp_query(netif, ipaddr, q);
    }

    /* continuation for multicast/broadcast destinations */
    /* obtain source Ethernet address of the given interface */
    /* send packet directly on the link */
    return etharp_send_ip(netif, q, (struct eth_addr*)(netif->hwaddr), dest);
}

/**
 * Send an ARP request for the given IP address and/or queue a packet.
 *
 * If the IP address was not yet in the cache, a pending ARP cache entry
 * is added and an ARP request is sent for the given address. The packet
 * is queued on this entry.
 *
 * If the IP address was already pending in the cache, a new ARP request
 * is sent for the given address. The packet is queued on this entry.
 *
 * If the IP address was already stable in the cache, and a packet is
 * given, it is directly sent and no ARP request is sent out.
 *
 * If the IP address was already stable in the cache, and no packet is
 * given, an ARP request is sent out.
 *
 * @param netif The lwIP network interface on which ipaddr
 * must be queried for.
 * @param ipaddr The IP address to be resolved.
 * @param q If non-NULL, a pbuf that must be delivered to the IP address.
 * q is not freed by this function.
 *
 * @note q must only be ONE packet, not a packet queue!
 *
 * @return
 * - ERR_BUF Could not make room for Ethernet header.
 * - ERR_MEM Hardware address unknown, and no more ARP entries available
 *   to query for address or queue the packet.
 * - ERR_MEM Could not queue packet due to memory shortage.
 * - ERR_RTE No route to destination (no gateway to external networks).
 * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
 *
 */
err_t
etharp_query(struct netif *netif, struct ip_addr *ipaddr, struct pbuf *q)
{
    struct eth_addr * srcaddr = (struct eth_addr*)netif->hwaddr;
    err_t result = ERR_MEM;
    s8_t i; /* ARP entry index */

    /* non-unicast address? */
    if (ip_addr_isbroadcast(ipaddr, netif) ||
        ip_addr_ismulticast(ipaddr) ||
        ip_addr_isany(ipaddr))
    {
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: will not add non-unicast IP address to ARP cache\n"));
        return ERR_ARG;
    }

    /* find entry in ARP cache, ask to create entry if queueing packet */
#if LWIP_NETIF_HWADDRHINT
    i = find_entry(ipaddr, ETHARP_TRY_HARD, netif);
#else /* LWIP_NETIF_HWADDRHINT */
    i = find_entry(ipaddr, ETHARP_TRY_HARD);
#endif /* LWIP_NETIF_HWADDRHINT */

    /* could not find or create entry? */
    if (i < 0)
    {
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not create ARP entry\n"));
        if (q)
        {
            LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: packet dropped\n"));
            ETHARP_STATS_INC(etharp.memerr);
        }
        return (err_t)i;
    }

    /* mark a fresh entry as pending (we just sent a request) */
    if (arp_table[i].state == ETHARP_STATE_EMPTY)
    {
        arp_table[i].state = ETHARP_STATE_PENDING;
    }

    /* { i is either a STABLE or (new or existing) PENDING entry } */
    LWIP_ASSERT("arp_table[i].state == PENDING or STABLE",
                ((arp_table[i].state == ETHARP_STATE_PENDING) ||
                 (arp_table[i].state == ETHARP_STATE_STABLE)));

    /* do we have a pending entry? or an implicit query request? */
    if ((arp_table[i].state == ETHARP_STATE_PENDING) || (q == NULL))
    {
        /* try to resolve it; send out ARP request */
        result = etharp_request(netif, ipaddr);
        if (result != ERR_OK)
        {
            /* ARP request couldn't be sent */
            /* We don't re-send arp request in etharp_tmr, but we still queue packets,
               since this failure could be temporary, and the next packet calling
               etharp_query again could lead to sending the queued packets. */
        }
    }

    /* packet given? */
    if (q != NULL)
    {
        /* stable entry? */
        if (arp_table[i].state == ETHARP_STATE_STABLE)
        {
            /* we have a valid IP->Ethernet address mapping */
            /* send the packet */
            result = etharp_send_ip(netif, q, srcaddr, &(arp_table[i].ethaddr));
            /* pending entry? (either just created or already pending */
        }
        else if (arp_table[i].state == ETHARP_STATE_PENDING)
        {
#if ARP_QUEUEING /* queue the given q packet */
            struct pbuf *p;
            int copy_needed = 0;
            /* IF q includes a PBUF_REF, PBUF_POOL or PBUF_RAM, we have no choice but
             * to copy the whole queue into a new PBUF_RAM (see bug #11400)
             * PBUF_ROMs can be left as they are, since ROM must not get changed. */
            p = q;
            while (p)
            {
                LWIP_ASSERT("no packet queues allowed!", (p->len != p->tot_len) || (p->next == 0));
                if (p->type != PBUF_ROM)
                {
                    copy_needed = 1;
                    break;
                }
                p = p->next;
            }
            if (copy_needed)
            {
                /* copy the whole packet into new pbufs */
                p = pbuf_alloc(PBUF_RAW, p->tot_len, PBUF_RAM);
                if (p != NULL)
                {
                    if (pbuf_copy(p, q) != ERR_OK)
                    {
                        pbuf_free(p);
                        p = NULL;
                    }
                }
            }
            else
            {
                /* referencing the old pbuf is enough */
                p = q;
                pbuf_ref(p);
            }
            /* packet could be taken over? */
            if (p != NULL)
            {
                /* queue packet ... */
                struct etharp_q_entry *new_entry;
                /* allocate a new arp queue entry */
                new_entry = memp_malloc(MEMP_ARP_QUEUE);
                if (new_entry != NULL)
                {
                    new_entry->next = 0;
                    new_entry->p = p;
                    if (arp_table[i].q != NULL)
                    {
                        /* queue was already existent, append the new entry to the end */
                        struct etharp_q_entry *r;
                        r = arp_table[i].q;
                        while (r->next != NULL)
                        {
                            r = r->next;
                        }
                        r->next = new_entry;
                    }
                    else
                    {
                        /* queue did not exist, first item in queue */
                        arp_table[i].q = new_entry;
                    }
                    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: queued packet %p on ARP entry %"S 16_F "\n", (void*)q, (s16_t)i));
                    result = ERR_OK;
                }
                else
                {
                    /* the pool MEMP_ARP_QUEUE is empty */
                    pbuf_free(p);
                    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not queue a copy of PBUF_REF packet %p (out of memory)\n", (void*)q));
                    /* { result == ERR_MEM } through initialization */
                }
            }
            else
            {
                ETHARP_STATS_INC(etharp.memerr);
                LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not queue a copy of PBUF_REF packet %p (out of memory)\n", (void*)q));
                /* { result == ERR_MEM } through initialization */
            }
#else       /* ARP_QUEUEING == 0 */
            /* q && state == PENDING && ARP_QUEUEING == 0 => result = ERR_MEM */
            /* { result == ERR_MEM } through initialization */
            LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: Ethernet destination address unknown, queueing disabled, packet %p dropped\n", (void*)q));
#endif
        }
    }
    return result;
}

/**
 * Send a raw ARP packet (opcode and all addresses can be modified)
 *
 * @param netif the lwip network interface on which to send the ARP packet
 * @param ethsrc_addr the source MAC address for the ethernet header
 * @param ethdst_addr the destination MAC address for the ethernet header
 * @param hwsrc_addr the source MAC address for the ARP protocol header
 * @param ipsrc_addr the source IP address for the ARP protocol header
 * @param hwdst_addr the destination MAC address for the ARP protocol header
 * @param ipdst_addr the destination IP address for the ARP protocol header
 * @param opcode the type of the ARP packet
 * @return ERR_OK if the ARP packet has been sent
 *         ERR_MEM if the ARP packet couldn't be allocated
 *         any other err_t on failure
 */
#if !LWIP_AUTOIP
static
#endif /* LWIP_AUTOIP */
err_t
etharp_raw(struct netif *netif, const struct eth_addr *ethsrc_addr,
           const struct eth_addr *ethdst_addr,
           const struct eth_addr *hwsrc_addr, const struct ip_addr *ipsrc_addr,
           const struct eth_addr *hwdst_addr, const struct ip_addr *ipdst_addr,
           const u16_t opcode)
{
    struct pbuf *p;
    err_t result = ERR_OK;
    u8_t k; /* ARP entry index */
    struct eth_hdr *ethhdr;
    struct etharp_hdr *hdr;

#if LWIP_AUTOIP
    const u8_t * ethdst_hwaddr;
#endif /* LWIP_AUTOIP */

    /* allocate a pbuf for the outgoing ARP request packet */
    p = pbuf_alloc(PBUF_RAW, SIZEOF_ETHARP_PACKET, PBUF_RAM);
    /* could allocate a pbuf for an ARP request? */
    if (p == NULL)
    {
        LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
                    ("etharp_raw: could not allocate pbuf for ARP request.\n"));
        ETHARP_STATS_INC(etharp.memerr);
        return ERR_MEM;
    }
    LWIP_ASSERT("check that first pbuf can hold struct etharp_hdr",
                (p->len >= SIZEOF_ETHARP_PACKET));

    ethhdr = p->payload;
    hdr = (struct etharp_hdr*)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_raw: sending raw ARP packet.\n"));
    hdr->opcode = htons(opcode);

    LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
                (netif->hwaddr_len == ETHARP_HWADDR_LEN));
    k = ETHARP_HWADDR_LEN;
#if LWIP_AUTOIP
    /* If we are using Link-Local, ARP packets must be broadcast on the
     * link layer. (See RFC3927 Section 2.5) */
    ethdst_hwaddr = ((netif->autoip != NULL) && (netif->autoip->state != AUTOIP_STATE_OFF)) ? (u8_t*)(ethbroadcast.addr) : ethdst_addr->addr;
#endif /* LWIP_AUTOIP */
       /* Write MAC-Addresses (combined loop for both headers) */
    while (k > 0)
    {
        k--;
        /* Write the ARP MAC-Addresses */
        hdr->shwaddr.addr[k] = hwsrc_addr->addr[k];
        hdr->dhwaddr.addr[k] = hwdst_addr->addr[k];
        /* Write the Ethernet MAC-Addresses */
#if LWIP_AUTOIP
        ethhdr->dest.addr[k] = ethdst_hwaddr[k];
#else   /* LWIP_AUTOIP */
        ethhdr->dest.addr[k] = ethdst_addr->addr[k];
#endif /* LWIP_AUTOIP */
        ethhdr->src.addr[k]  = ethsrc_addr->addr[k];
    }
    hdr->sipaddr = *(struct ip_addr2*)ipsrc_addr;
    hdr->dipaddr = *(struct ip_addr2*)ipdst_addr;

    hdr->hwtype = htons(HWTYPE_ETHERNET);
    hdr->proto = htons(ETHTYPE_IP);
    /* set hwlen and protolen together */
    hdr->_hwlen_protolen = htons((ETHARP_HWADDR_LEN << 8) | sizeof(struct ip_addr));

    ethhdr->type = htons(ETHTYPE_ARP);
    /* send ARP query */
    result = netif->linkoutput(netif, p);
    ETHARP_STATS_INC(etharp.xmit);
    /* free ARP query packet */
    pbuf_free(p);
    p = NULL;
    /* could not allocate pbuf for ARP request */

    return result;
}

/**
 * Send an ARP request packet asking for ipaddr.
 *
 * @param netif the lwip network interface on which to send the request
 * @param ipaddr the IP address for which to ask
 * @return ERR_OK if the request has been sent
 *         ERR_MEM if the ARP packet couldn't be allocated
 *         any other err_t on failure
 */
err_t
etharp_request(struct netif *netif, struct ip_addr *ipaddr)
{
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_request: sending ARP request.\n"));
    return etharp_raw(netif, (struct eth_addr*)netif->hwaddr, &ethbroadcast,
                      (struct eth_addr*)netif->hwaddr, &netif->ip_addr, &ethzero,
                      ipaddr, ARP_REQUEST);
}

/**
 * Process received ethernet frames. Using this function instead of directly
 * calling ip_input and passing ARP frames through etharp in ethernetif_input,
 * the ARP cache is protected from concurrent access.
 *
 * @param p the recevied packet, p->payload pointing to the ethernet header
 * @param netif the network interface on which the packet was received
 */
err_t
ethernet_input(struct pbuf *p, struct netif *netif)
{
    struct eth_hdr* ethhdr;
    u16_t type;

    /* points to packet payload, which starts with an Ethernet header */
    ethhdr = p->payload;
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE,
                ("ethernet_input: dest:%02x:%02x:%02x:%02x:%02x:%02x, src:%02x:%02x:%02x:%02x:%02x:%02x, type:%2hx\n",
                 (unsigned)ethhdr->dest.addr[0], (unsigned)ethhdr->dest.addr[1], (unsigned)ethhdr->dest.addr[2],
                 (unsigned)ethhdr->dest.addr[3], (unsigned)ethhdr->dest.addr[4], (unsigned)ethhdr->dest.addr[5],
                 (unsigned)ethhdr->src.addr[0], (unsigned)ethhdr->src.addr[1], (unsigned)ethhdr->src.addr[2],
                 (unsigned)ethhdr->src.addr[3], (unsigned)ethhdr->src.addr[4], (unsigned)ethhdr->src.addr[5],
                 (unsigned)htons(ethhdr->type)));

    type = htons(ethhdr->type);
#if ETHARP_SUPPORT_VLAN
    if (type == ETHTYPE_VLAN)
    {
        struct eth_vlan_hdr *vlan = (struct eth_vlan_hdr*)(((char*)ethhdr) + SIZEOF_ETH_HDR);
#ifdef ETHARP_VLAN_CHECK /* if not, allow all VLANs */
        if (VLAN_ID(vlan) != ETHARP_VLAN_CHECK)
        {
            /* silently ignore this packet: not for our VLAN */
            pbuf_free(p);
            return ERR_OK;
        }
#endif  /* ETHARP_VLAN_CHECK */
        type = htons(vlan->tpid);
    }
#endif /* ETHARP_SUPPORT_VLAN */

    switch (type)
    {
    /* IP packet? */
    case ETHTYPE_IP:
#if ETHARP_TRUST_IP_MAC
        /* update ARP table */
        etharp_ip_input(netif, p);
#endif  /* ETHARP_TRUST_IP_MAC */
        /* skip Ethernet header */
        if (pbuf_header(p, -(s16_t)SIZEOF_ETH_HDR))
        {
            LWIP_ASSERT("Can't move over header in packet", 0);
            pbuf_free(p);
            p = NULL;
        }
        else
        {
            /* pass to IP layer */
            ip_input(p, netif);
        }
        break;

    case ETHTYPE_ARP:
        /* pass p to ARP module */
        etharp_arp_input(netif, (struct eth_addr*)(netif->hwaddr), p);
        break;

#if PPPOE_SUPPORT
    case ETHTYPE_PPPOEDISC: /* PPP Over Ethernet Discovery Stage */
        pppoe_disc_input(netif, p);
        break;

    case ETHTYPE_PPPOE: /* PPP Over Ethernet Session Stage */
        pppoe_data_input(netif, p);
        break;
#endif  /* PPPOE_SUPPORT */

    default:
        ETHARP_STATS_INC(etharp.proterr);
        ETHARP_STATS_INC(etharp.drop);
        pbuf_free(p);
        p = NULL;
        break;
    }

    /* This means the pbuf is freed or consumed,
       so the caller doesn't have to free it again */
    return ERR_OK;
}
#endif /* LWIP_ARP */
